Method of bonding



June 2, 1953 N. LANGr-:R 2,640,798

METHQD 0F BoNDIN'G Filed Feb. 27, 1951 2 sheets-'sheet 1 INVTOR.

June 2, 1953 N. LANGER 2,640,798

METHOD 0F BONDI'NG Filed Feb. 27. 1951 2 Sheets-Sheet 2 1| INVENToR.

Patented June 2, 1953 .T1

Application February 27, 1951, Serial No. 212,880

14 Claims.

This invention relates to machines and methods for bonding or sealing together a plurality of plies r layers of thermoplastic sheet material.

In recent years various bonding machines have been introduced for bonding together plies of thermoplastic material by electrostatic heating of the material in a high frequency eld. The operation of these machines is based on passing the superposed plies of the thermoplastic material through the space between a pair of electrodes connected to a source of radio frequency energy, the displacement of such plies being effected in a step-by-stepl or discontinuous manner,

such as in a conventional sewing machine, or in a continuous manner, such as by means of a pair of feed rolls. The powerful high frequency field Aproduced in the electrode zone will heat up the plies of the material passing therethrough to their bonding temperature, causing sealing or bonding of such plies as a result of the joint effect of heat and electrode pressure.

While electrostatic bonding machines of the described character, sometimes referred to in the industry as electronic sewing machines, have lbeen used in the industry for some years on a rather limited scale, their use on a large scale in the quantity production of articles formed 4from thermoplastic sheet material was greatly handicapped and in many cases was completely prevented by a combination of the following factors:

(1) The operation of conventional electronic sewing machines is based on the heat produced in the material as a result of dielectric losses in a high frequency eld. This introduces certain inherent limitations as to the types of thermoplastic materials which may be successfully bonded and obviously excludes such materials in which the dielectric losses are very low. It so happens, that there are various materials, such as particularly polyethylene, which are characterized by an extremely low loss factor, although they are quite desirable for other reasons, such as low cost, high strength, chemical inertness, low gas permeability, and the like..

(2) In View of the extremely high frequencies used in electrostatic bonding machines, serious problems are introduced in connection with impedance matching, in controlling the amount of heat generated in the plies, etc. Even very minute and frequently unavoidable variations in the composition and thickness of the plies or in the rate feeding the plies past the electrodes may prevent the.` production of uniformly sound seals or bonds.

(3) The amount of high frequency energy required is quite considerable and the equipment necessary for generating such energy is bulky and expensive both to build and to operate. As a result, the initial cost of these electrostatic where no other method of bonding will serve.

,.tion;

may be solved and the foregoing disadvantages may be eliminated in` a remarkably simple manner.

It is an object of the present invention to improve electronic bonding machines.

It is another object of the present invention to provide a novel and improved electronic bonding machine and method of the thermal impulse type.

It is a further object of the present invention to provide a novel machine and method for bonding together plies of thermoplastic sheet material in which an electrically conducting thread or filament is combined with linear regions'of the plies by passing heating pulses of current through limited lengths of such filament.

It is also within the contemplation of the invention to provide an electronic bonding machine which does not require any high frequency currents for its operation but may be operated with alternating currents of commercial power line frequencies.

The invention also contemplates an electronic bonding machine which is simple and inexpensive to construct and to operate and which may be manufactured and sold at a fraction of the cost of conventional electronic bonding machines of the high frequency electrostatic type. y

Other and further objects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings; in which Fig. 1 is a side elevation, somewhat diagramtronic bonding machine embodying the principles K of the invention;

Fig. 2 `is a front View of a portion of the machine shown in Fig. l; v

Fig. 3 is a fragmentary top plan View of two layersof thermoplastic sheet material bonded together in accordance with my present inven- Fig. 4 is a sectiontaken on line ll--ll of Figure3;

Fig. 5 is a view similar to Figure 1 but showing a modified form of my invention.

Fig. 6-is a front elevation of the apparatus shown in Figure 5;

Fig. 7 isa fragmentary top plan view of two layers of thermoplastic sheet material bonded together by means of the apparatus 4shown in Figures 5 and 6; and

Fig. 8 is a section taken on line 8 8 of Figure 7.

The present application is a continuation-inpart of my co-.pending application Serial No.

.104,775,1led July 14, A1949, for Method of Heatsealing and constitutes an improvement over the heatsealing machines and vmethods disclosed and claimed in my U. S. Patents Nos. 2,460,460 and 2,479,375. y

Broadly considered, in accordance with the principles of my invention, the layers or plies of thermoplastic sheet material to be bonded together are brought into face-to-face superposed position and into contact with an electrically conducting elongated member, such as a thin strip, band, thread, or filament. The structure constituted by said layers and said filament is then passed through a pressure zone wherein a limited length of the structure is placed under compression and at the same time a pulse of an electric current is passed through the corresponding length of the filament. This pulse of current will heat the said lengths of the filament and the region of the thermoplastic layers in contact therewith to heatsealing temperature, practically instantaneously. rihe combined effect of heat and pressure in the pressure zone will cause heat sealing or bonding of the layers, at the same time partially or fully embedding the lament in the bonded region, thereby producing a stitch Further portions or lengths of the thermoplastic layers with the superposed conducting filament are advanced into the pressure or bonding zone in a continuous or discontinuous manner and the procedure is repeated to progressively form a series of closely spaced or even continuously merging stitches in the layers. Advantageously, in each sealing or bonding cycle, the duration of the pulse of sealing current is so controlled as to be shorter than that of the application of pressure so that each stitch may be permitted to cool and to consolidate while still under pressure. In this manner, the maximum strength of the produced bond is obtained, as it will be set forth more fully hereinafter.

Referring now more particularly to Figs. i and 2 of the drawing, reference numeral ID denotes the head of suitable reciprocating mechanism, such as the one found in conventional sewing machines. This mechanism actuates a. reciprocating bar II and a pressure foot I2 in predetermined sequence, the said pressure foot cooperating with a feed dog I3 to advance the layers of thermoplastic material interposed therebetween. In view of the fact that the reciprocating mechanism and bar and the pressure vfoot and feed dog are conventional in structure,l and their operation is well known to those skilled in the art, no detailed description thereof will be necessary, particularly as they do not form part of the present invention.

At the lower end of reciprocating bar II, there is secured a sealing member or bar, generally denoted by reference numeral I4, by means of a screw I5. Sealing member i4 is in the form of a narrow elongated piece I6 of insulating material of great mechanical strength, such as a suitable synthetic resin. A pair of metallic electrodes I'I and I3 are molded or embedded in piece IE of insulating material so that their smooth lower surface is flush with that of the insulating material and constitutes the pressure surface of the sealing member or bar. It will be noted that the width of the sealing member is less than the space between the two arms I8 and 2U of pressure foot I2 so that the said member may be reciprocated between the two arms during operation of the machine, much in the same way as the needle of a conventional sewing machine. A shallow, semi-circular longitudinal groove 2I extends along the length of the pressure face of the sealing member, including the exposed surfaces of electrodes I1 and I8 and serves for guiding an electrically conducting thread or filament 22 in the proper cooperating relation with layers 23 and 24 of thermoplastic sheet material.

The top or operating surface of feed dog I3 is covered with a layer 25 of a suitable elastomer, such as of silicone rubber, constituting a pressure member, the working face of which is arranged for cooperation with the working face of the sealing member I4 and as a result of its surface characteristics is adapted for frictional engagement with layer 24 of the thermoplastic sheet material.

The electrical system of the machine comprises a step-down transformer 26, having a primary, or high-voltage winding 21 and a secondary or low-voltage winding 28. The ends of secondary winding 28 are respectively connected to electrodes Il and I8 through lead wires 29 and 30 and through resilient spiral conductors 3| and 32 so that such electrical connection is maintained during the reciprocation of sealing member I4.

The primary winding 2'! of transformer 26 has one of its ends directly connected to terminal 33 and its other end is connected to terminal 34 of a source of alternating current of commercial power line frequency through a time-delay switch 35, rheostat 44, and an on-oil switch 36. Actuating plunger 31 of time-delay switch 35 is operable by means of an actuating rod 38, mounted on the upper portion of reciprocating bar II. The time when operation of the time delay switch 35 is initiated during downward displacement of reciprocating bar II is adjustable by means of set screw 39 depending from the end of actuating rod 38 and the length of the period after which the said switch is automatically disabled or opened is adjustable by means of screw 40. In view of the fact that time delay switches of various types adaptable to the purposes of the present invention are wellknown to those skilled in the art, the said switch has been merely diagrammatically indicated in the drawing. For a detailed description of such switches reference may be had, for example, to my Patents 2,460,460 and 2,479,375.

The electrically conducting thread or filament 22 is drawn from a spool 4I over a guide roll 42 and through an apertured guide member 43 mounted on the side of sealing member I4. Great variations are possible in the material of the thread or filament. lt may be in the form of a thin, highly flexible metal wire having appreciable strength, such as copper, aluminum, steel or iron wire, and the like. In general, wires formed of metals or alloys of high specific resistivity are preferred for reasons which will appear presently. IThus. thin wires formed of high resistance alloys, such as a nickel-chromium alloy known in the trade as Nichrorne are excellent both from the point of View of high resistivity and high tensile strength but are relatively expensive. A good compromise may be found in using iron or steel wire, such as iron or steel wire coated or plated with copper, nickel. tin or zinc, which is inexpensive but combines relatively high resistivity with satisfactory tensile strength and good surface characteristics.

Other materials suitable for the purposes of the invention are synthetic filaments of an electrically conducting character, such as Elements extruded from cellulose derivatives, rubber hydrochloride, vinyl resins, vinylidene chloride, polyethylene. These materials, which are normally good dielectrics, are rendered electrically con- 'ducting by the incorporation of substantial proportions of carbon or graphite particles, or of a suitable finely divided metal powder. Particularly good results are obtained when the electrically conducting synthetic filaments are made of a material having approximately the same melting or softening temperature as the thermoplastic sheet materials to be bonded together.

For example, sheets of polyethylene may be advantageously bonded by means of filaments extruded from va mass of polyethylene, which was rendered electrically conducting by the admixture of :finely divided carbon, graphite, or metal particles.

A satisfactory and very inexpensive electrically conducting filament is provided by a conventional sewing thread of textile fibres which is impregnated or coated with carbonaceous material. While threads of this type are not readily obtainable in commerce at the present time, they are easily produced, for example by passing a conventional sewing thread through a colloidal graphite solution, such as the colloidal graphite preparation rknown under the name Aquadag, or by impregnating or coating the thread with such preparation in some other suitable manner.

From the foregoing description, the operation of the bonding machine of the invention will be readily understood by those skilled in the art.

When beginning the bonding operation, the layers 23 and 24 of thermoplastic sheet material to be bonded together are placed in face-to-face position on surface of the machine and pressure foot I2 is manually set into its operative position, holding the said layers against surface 25. The end of electrically conducting filament 22 is now placed in and along the groove 2I of sealing member or bai- I4. The reciprocating mechanism of the machine is now manually advanced downwardly until reciprocating bar II and sealing bar I4 with the end of filament 22 underneath will be passed through arms I9 and 20 of the pressure foot and pressed against the surface of layers 23 and 24. It will be noted that in this position of the several elements, electrodes I1 and I8 of the sealing member will be pressed into electrical contact with the interposed unit length of the conducting filament. During the downward displacement of reciprocating bar II, screw 39 will depress actuating plunger 31 of time delay switch 35. This, however, will not result in energizing transformer 26 due to the fact that main line switch 36 is still open. Switch 36 is now closed so that the primary winding 21 of transformer 26 is energized from alternating curv rent source 33, 34, main switch 36, rheostat 44, and preset time delay switch 35. The time delay switch is so constructed and arranged as to maintain the circuit closed only for a predetermined short period of time, generally in the order of a fraction of a second, and thereafter to automatically open the said circuit. During the period while the circuit is closed, a low voltage pulse of alternating current of relatively high intensity will be produced in the secondary circuit, comprising secondary winding 28, conductors 29, 30, 3| and 32, electrodes I1 and I8 and the interposed unit length of conducting filament 22. The extremely short but powerful pulse of current will practically instantaneously heat the said length of filament to or even considerably above the heat sealing or bonding temperature of layers 23 and 24. The heat thus generated is transferred by surface contact to the underlying region of the said layers causing heat sealing thereof. As a result, the unit length of the conducting filament will be embedded into one or both of the underlying layers and upon cooling will form a strong bond therewith. In the following such unit length of the conducting filament bonded to two layers of thermoplastic film will be referred to as a stitch As a result of the manually executed preparatory steps described in the foregoing, the end of the conducting filament has been securely bonded to the first stitch or bond formed in the thermoplastic layers. Thus, when the said layers are now displaced in the direction of arrow by the length of the "stitch due to the conventional cooperation of pressure foot I2 and feed dog I3, a further unit length of the said conducting filament will be pulled from spool 4I, through guide roller 42 and guide member 43.

The bonding machine is now ready for the automatic operation, by actuating the driving means including an electric motor and the various mechanical devices driven thereby whereby reciprocating bar II, pressure foot I2 and feed dog I3 are operated in properly timed sequence in a manner similar to the operation of a conventional power-driven sewing machine. During this automatic operation, the following steps are carried out cyclically and in very rapid succession:

(l) Pressure foot I 2 is lowered to hold down layers 23 and 24 against surface 25 of feed dog I3.

(2) Reciprocating bar II is lowered, thereby pressing the pressure member I4 and the underlying unit length of conducting filament 22 against the portion of the upper thermoplastic layer 23 exposed between the arms I9 and 20 of pressure foot I2. In this position, the ends of said unit length of the conducting filament 22 are in electrical contact with electrodes I1 and I I8 of pressure member I4.

(3) Shortly before or immediately after the pressure member I4 has reached its pressure-applying position, set screw 39 will be displaced downwardly by means of actuating rod 38, concurrently with the downward displacement of reciprocating rod II and the said set screw will strike against actuating plunger 31 of time delay switch 35.

(4) Operation of the time delay switch 35 is initiated, the said switch being of the type which closes an electric circuit at once and opens the said circuit automatically, after a predetermined and adjustable time delay period.

(5) The primary circuit, including terminal 34 of the alternating current power line, main switch 36, time delay switch 35, rheostat 44, primary winding 21, and terminal 33 of the power line, is now energized. This will induce a lowvoltage high-intensity current in the secondary circuit comprisingsecondary winding 28, conductors 29, 30, 3l, 32, electrodes Il and I8, and the unit length of conductive filament 22 between said. electrodes.

(6) The heavy current flowing through the unit length of filament will heat the said length to a relatively high temperature, such temperature being reached practically instantaneously due to the low heat capacity of the filament. The heat thus produced is rapidly conducted by surface contact and conduction into the corresponding region of the underlying thermoplastic layers 23 and 24. As a result of the combined effect of heat and pressure. a stitch is formed in the said region, in which stitch the unit length of (8) Reciprcca ng rod i! is now raised, lifting up sealing nie ler i4 from the completed ,stitch."`

(9) Feed dos i3 i face 25 enge fr: no

actuated, its operative sur- -n some friction the lower avc-r 2li, thereby advancing a new lei s 23 and 721i or" Element 22 into stit 'ug position, whereupon the entire cycle is repeated. over and over again so long the in :chine maintained in operation and d with ilrns of thermoplastic material electrically conducting thread. Figs. 3 and 4 show L4herir-oplastic layers 23 and 24 bonded together' by the machine and forming a unitary product with the electrically conducting thread lt will be noted that the external appearance o1? the bonded product is not unlilre to that of a pair of layers stitched together hr means of e co. ventional sewing niachine. However, the actual bond between the layers is formed by fusion of the layers in the line 46 and not by the locling eii'ect of thread itself. As a matter or" fact, in scrne cases, the

electrically conducting thread may be separated from or may he peeed ofi from the finished bonded product.

While in Fig. fithe. line of fusion hond t5 shown as succession of spaced stitches such unit lengths of fusion bond may be caused to merge into each other appropriate control of the bonding cycle, particularly by making the unit length by which the materials are advanced after each stitch less than the length that is bende-:l together' during each bonding cycle. This will cause the successive stitches to overlap and to merge into ch other.

The bonding machine of the invention just described operates in a cyclic or reciprocating manner, that is, the materials to be bonded are advanced through the bonding station step-by-step. In some cases however, it is advantageous to carry out the bonding process upon a continuously displaced Wiaterial. such inode of operation being adaptalle to higher operating speeds. A bonding machine suitable for this Inode of operation will now be described with reference to Figs. 5 and 6 of the drawing.

The most importent element of this modified embodiment or' the invention is a bonding un or roll, generally denoted by reference numeral 5l. As it will best appear from Fig. 6, this wheel comprises a pair or" rnetal discs 52 and 53, each having pluralities of integerally formed teeth, 54 and respectively, uniformly spaced around the circumference thereof, such teeth alternately extending into their respective interspaces. The interspaces are lled with heat-resistant insulatn ine material and the entire struct-ure is turned oo n smooth in lathe to produce a smooth circumferential face in which toot`n-lilre metal segments or electrodes are embedded, such segments being alternately connected electricall,7 with discs 52 and 53, respectively. It is preferred to nzachine a smell depression or groove 56 into the circumferential face of the bonding wheel for positively gi lding an electrically conducting filament or thread 59 therein, Brushes 57 and 58 are arranged in sliding Contact with metal discs 53, respectively, r with suitable slipring-like extensions thereof. It will thus be noted that each of the said brushes is in continuous electrical contact with one half of the metal segments or electrodes 54, 55, on the circumference of the bonding wheel, the segments of the two groups alternating with each other.

Bonding .vheel or roll 5l cooperates with a pressure wheel or roll 55., .sui able conventional driving mechanism (not shown) being provided for driving the wheels ,roll An opposite directions, thereby contii fencing layers 52, 63 of thermoplastic illv nith the electrically conducting thread 5S superposed ,reon, on iced table fifi through t7 eight ci? the tv eels cr rolls.

'cuit the bonding machine -do2vn transformer 65 having a secon-:lary or lo .l voltage winding 5G, the ends of which respectively connected with brushes 5.' and 58. One end of the primary winding f2.1 of

said transformer directly connected to one terof .source of alternating current 6B of power line frequency, while the other end of the ci a. e delay relay generally denoted by reference numeral 1U.

The control nirc'iit of the machine comprises l ce. .ct l! and 12,1especcar" g cooperating contacts 73 and 14. t sri ig ll directly connected to one of terminals or alternating current source S8, o Contact swing l?. is connected to the other iinal o s source through the actuating electromag t 7" of the ne delay relay l0. The time delay rela, is or" the well-known conventional type being so constructed and arran 'ed that upon energizing eleotromagrct 75 for :ort period, contacts '59 d such conne-ts are reopened automatically after a. predetermined time delay period and tio rela; is reset for the next operating cycle. The length of the time delay period may be manually adjusted by adjustment screw or knob 16.

Leaf spring .T2 is "tended further than spring,y 'H and carries at its ee end a small roller l1 which rides on the circumference of acam disc 18 having uniformly spaced protuberances or teeth 1s thereon. Cam disc is is mechanically connected. to bonding wheel 5i for joint rotation therewith through a shaft or similar mechanical connection diagi'ainniatically indicated by dotted line 89. The number of protuberances or teeth on cam disc I8 equals in number the combined num or segments 55 and 55 on bonding Wheel and their angular arrangement is so adjusted with respect to that of the said segments that cam follower roller 'il is lifted up upon or shortly after a pair of adjoining segments in groups 54 and 55 being pressed against and brought into electrical Contact with a unit length of the electrically conducting thread 59.

The electr'cally conducting thread 55 is unwound from a sup y roll or bobbin Bi, rotatably supported on a spindle 82. and is guided around guide rolls 83 and 84 to groove 56 of bonding wheel 5i and into cooperating bonding relation with layers of thermoplastic material 62 and 63.

The operation of this modified embodiment of the invention is as follows:

Layers 52 and E3 of the thermoplastic material, with the free end. of the electrically conducting thread 59 superposed thereon, are placed on feed table 64 between bonding wheel 5l and pressure Wheel Bl, the said thread being placed into circumferential groove 56 of the bonding wheel. The driving means are then actuated, causing continuous rotation of wheels l and 6l in opposite directions and continuous advancement of the thermoplastic layers and superposed thread. Cam disc 18 will also be rotated in the same direction and at the same angular velocity as bonding wheel 5l. `The following cycle or sequence of operations will now take place:

(l) A pair of adjacent contact segments from groups 54 and 55, respectively, will be pressed against a unit length of thread 59 that happens to be in the bight of wheels 5I, 6l, thus electrically connecting such unit length to the ends of secondary winding 66 of transformer 65 through brushes 51 and 58, which slide on the slip rings integrally formed with metal discs 52 and 53, respectively. i

(2) Approximately at the same time, roller 11 will be lifted up by one of the protuberances 19 of cam disc 1t, closing the control circuit of the machine between contacts 13 and 14, thus completing the circuit of electromagnet 15. Upon being energized, the electromagnet initiates the operation of time delay relay 10. The relay closes its operating contacts 99 which connect the primary winding 61 of transformer E5 directly to alternating current source 68.

3) A pulse of low-voltage alternating current of high intensity is induced in secondary windings 66 and is caused to flow in the secondary circuit including winding 66, brushes 51, 58, contact segments 54, 55 and the unit length of electrically conducting thread 59 under compression. The heat generated in the said unit length is transferred by surface contact to the underlying linear region of thermoplastic layers 62 and 63, causing fusion and bonding or heatsealing thereof at their interface.

(4) A predetermined but extremely short period thereafter, the time delay relay automatically breaks the primary circuit between contacts 69, discontinuing the generation of sealing heat in the bonding zone. Preferably, the period of heat generation is so adjusted as to be somewhat shorter than the period of pressure application thereby allowing the bond or stitch formed to cool and set under pressure.

(5) A new unit length of the thermoplastic layers 52, 63 and of thread 59 is advanced into the bonding zone and the cycle is repeated.

Of course, the entire cycle takes place within a small fraction of a second so that relatively high linear bonding speeds may be obtained.

In some cases, particularly when high operating speeds are used, the proper coordination of the period during which transformer 65 is energized to the period of pressure application may be accomplished merely by giving a suitable shape to teeth or protuberances 19 of cam disc 1B. In that case relay 19 may be simply an ordinary switching relay, rather than a time delay relay.

Figs. '7 and 8 illustrate the appearance of the bonded product of the bonding machine shown in Figs. 5 and 6. It will be noted that the product comprises a pair of layers 62 and 63 of thermoplastic material which are fused together in their interface along a linear region 85, the electrically conducting thread 59 being partially or fully embedded into one or both of the said layers. While the heatsealing operation is carried out progressively for unit lengths of the materials, the resulting stitches or elementary bonds are so closely spaced or are even overlapping with respect to each other that they result in a linear bond which is for all practical purposes continuous and fluid-tight. In some cases when the electrically conducting thread 59 is of suflicient tensile strength and its diameter is substantial as compared to the combined thicknesses of the thermoplastic layers 62, G3, the thread is capable of functioning as a tearing strip, in other words the removal or stripping off of the thread from the bonded article, which may, for example, be a sealed bag, will cause opening of the sealed bond or at least considerable weakening thereof. Where such operation of the thread is intended, it is desirable to leave a length of the thread freely extending beyond the bonded layers, such length being adapted to be gripped by the fingers for carrying out the tearing or stripping operation. Otherwise, of course, the said thread is cut off approximately at the point where the thermoplastic layers end, after completion of the bonding operation, much in the same way as the thread is cut or broken off after two pieces of fabric or other sheet material have been stitched together by means of a conventional sewing machine.

While the machines and methods of the invention have been described and illustrated with particular reference to bonding together two layers or plies of thermoplastic material, they are obviously applicable with equal or similar results to the bonding of three or more plies of such materials.

What is claimed is:

l. The method of heat sealing layers of thermoplastic material which comprises bringing regions of the layers to be heat sealed into facetO-face superposed position, pressing an elongated electrically conducting member against said region of the layers, and passing an electric current through said member to cause heating thereof and of the region of the layers in contact therewith to heat sealing temperatures and permanent bonding of said member and of said thermoplastic layers into a single heat sealed structure.

2. The method of heat sealing layers of thermoplastic material which comprises applying onto the region of the layers to be heat sealed an elongated self-sustaining electrically conducting strip, passing a current pulse through said strip, said current having suilicient intensity and duration to heat said strip and the said region of the layers to heat sealing temperature and to cause permanent bonding of said region of the layers into a structure in which said conducting strip is at least partially embedded.

3. The method of heat sealing layers of thermoplastic material which comprises applying under compression onto the region of the layers to be heat sealed an elongated thread formed of electrically conducting material, passing an electric current pulse through said thread, adjusting the intensity and duration of said current pulse to heat said region of the layers to heat sealing temperature, and maintaining the compression on the said thread and said region of the layers until said region has cooled and consolidated and is permanently bonded together and to said thread.

4. The method of heat sealing layers of thermoplastic material which comprises compressing with a linear region of the layers a thread of conducting thermoplastic material, passing an electric current pulse through thread, adjusting the intensity and duration o said pulse to heat said thread and said region of the layers in contact therewith 'to heat sealing temperature, and maintaining the compression on the said thread and said region of the layers until they have cooled and consolidated and are permanently fused together into an integral structure.

5. The method deiined in claim 4 wherein the fusion temperature or" the thermoplastic layers and of the conducti thermoplastic thread are approximately the saine.

G. The method of heat sealing layers of thermoplastic material which comprises compressing with a linear region of limited length of the layers a corresponding length oi a thread of electrically conducting material, passing through said length of the thread a pulse of electric current having suol intensity and duration as to cause at least ai fusion of the layers in said ing the lompression on said thread until the layers artially consolidated and have been. permanently bonded together, and then advancing a new region of said layers and of said thread into compressed relation and repeating thereon the same procedure.

7. The method. of heat sealing layers of thermoplastic material which comprises bringing the layers into ace-to-face position and into contact with an electrically conducting filament, passing the structure constituted by said layers and said filament through a compression station, dissipating an electric current in a portion of said filament 'to heat the said portion and the layers in contact therewith to heat sealing temperature while under compression thereby forming a stitch wherein said portion of the filament and the layers in contact therewith are bonded together, and continuously advancing further portions ci said iilament and of said layers through said compression station to progressively form a series of closely spaced stitches in said layers.

8. The method of heat sealing layers of thermoplastic material which comprises bringing the layers into iace-to-face position, superposing onto said layers an electrically conducting rilament, advancing the resulting structure through the bight of a pair of compression rolls, and passing an electric current through a length of said filament substantially r-.fit'nin the bight of said rolls to heat such length to a temperature which will cause heat sealing oi the layers to each other and to said heated length of filament.

9. The method of heat sealing layers of thermoplastic materia-l .vhich comprises progressively combining the layers to be heat sealed with an electrically conducting nlament into alaminar structure, continuously advancing said structure through the bight of a pair of compression rolls, and continuously passing an electric current through a progressively advancing length of said iilament that is adjacent to the bight of the rolls, said current having such intensity as to cause heat sealing oi a portion or" the thermoplastic layers together and with said preheated length oi" illament upon their compression in the bight of said rolls thereby causing the ejection from the bight of said rolls of the bonded layers joined together by a continuous linear seam.

10. The method of heat sealing layers of thermoplastic material which comprises progressively superposing onto the layers to be heat sealed an electrically conducting filament to constitute e composite structure, continuously advancing said structure through the bight of a pair of compression rolls, and passing a train of electric current pulses through a progressively advancing length of said filament that is adjacent to the bight of the rolls, said current pulses having such intensity and their frequency and duration being so related to the displacement of said stmoture through said rolls as to cause heat sealing of a portion of the thermoplastic layers together with each other and with said preheated length of filament upon their compression in the blght of said rolls thereby causing the ejection from the bight of said rolls of the bonded layers joined together by a stitchsimul`ating intermittent linear seam.

11. The method of bonding together two layers of thermoplastic material which comprises heating a thread-like member to the bonding temperature of the layers, and bringing said member into pressure contact with the regions of the layers to be bonded thereby to cause heating of such regions and bonding thereoi` into a composite structure with said member.

12. The method of bonding together two layers of thermoplastic material which comprises progressively preheating successive portions of a thread to the bonding temperature of the layers, and progressively bringing such preheated portions of the threadY into pressure contact with the regions of the layers to be bonded together thereby to cause heating and bonding of said regions.

13. The method of bonding together two layers of thermoplastic material which comprises progressively dissipating electrical energy in successive portions of a thread to heat such portions to the bonding temperature of the layers, and progressively bringing such heated portions of the thread into heat exchange relation with the regions of the layers to be bonded together to cause heating and bonding of said regions.

14. The method of bonding together two layers of thermoplastic material which comprises progressively exposing successive portions of a thread to the heating effect of an alternating electric current to heat such portions t0 the bonding temperature of the layers, and progressively bringing such heated portions of the thread into pressure and heat exchange relation with linear regions of the layers to be bonded together to cause heating and bonding of said regions.

NICHOLAS LANGER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 553,328 Aylsworth Jan. 21, 1896 1,148,189 Perris July 27, 1915 1,327,281 Jenkins Jan. 6, 1920 1,602,870 Villiers Oct. 12, 1926 1,972,942 Meyercord Sept. 11, 1934 2,327,972 Stettinlus et al Aug. 24, 1943 2,393,100 Gallay Jan. 15, 1946 2,500,053 Andrews Mar. 7, 1950 2,521,661 Williams Sept. 5, 1950 2,546,164 Norris Mar. 27, 1951 2,556,008 Spalding June 5, 1951 2,556,609 Arkless June 12, 1951 

1. THE METHOD OF HEAT SEALING LAYERS OF THERMOPLASTIC MATERIAL WHICH COMPRISES BRINGING REGIONS OF THE LAYERS TO BE HEAT SEALED INTO FACETO-FACE SUPERPOSED POSITION, PRESSING AN ELONGATED ELECTRICALLY CONDUCTING MEMBER AGAINST SAID REGION OF THE LAYERS, AND PASSING AN ELECTRIC CURRENT THROUGH SAID MEMBER TO CAUSE HEATING THEREOF AND OF THE REGION OF THE LAYERS IN CONTACT THEREWITH TO HEAT SEALING TEMPERATURES AND PERMANENT BONDING OF SAID MEMBER AND OF SAID 